1. Field of the Invention
This invention relates to video signal processing technology, more particularly to an image detecting device and method for detecting image positions.
2. Description of the Related Art
A digital television provides an aspect ratio of 16:9 for effectively expanding a viewing range. Since video signal frames are created in a 4:3 aspect ratio format to comply with conventional analog televisions, appropriate size conversion processing is required to present the video signal frames on a widescreen television. Likewise, high-definition video signal frames created in a 6:9 aspect ratio format are required to undergo appropriate size conversion processing to be displayed on conventional analog televisions.
Referring to FIG. 1, conventional size conversion processing involves scaling an original frame 7. However, since it typically cannot match a desired aspect ratio, black blanks are used for compensation. As a result, the processed video signal frame usually comprises image content (or image portion) 81 and blank content (or blank portion) 82.
Interlaced scanning involves separating a frame into even and odd fields for transmission. When a multimedia chip receives an interlaced video signal, the multimedia chip performs de-interlacing processing of the interlaced video signal before the latter can be shown on a display panel. De-interlacing processing normally involves dynamic compensation and interpolation processing using adjacent fields. If the positions of the image portion 81 and the blank portion 82 are not known in advance, it is possible that the image portion 81 of one field and the blank portion 82 of another field would be subjected to computational processing, thereby resulting in incorrect dynamic compensation and interpolation.
Moreover, when the multimedia chip performs other image processing that requires feedback computations, current and previous fields/frames are compared. If an image portion 81 of a field/frame is cross-processed with a blank portion 82 of another field/frame, defects arise, such as noise. Therefore, it is desirable to know the positions of the image portion 81 and the blank portion 82 of a frame before de-interlacing processing or other image processing tasks are performed.